Field of the Invention
The present invention relates to a thin film solar cell structure which causes two or more reflections for an vertically incident sunlight and thus more photovoltaic conversions are produced by every single vertically incident light. More electric power is therefore generated and the photovoltaic conversion efficiency is improved.
Description of Related Art
Solar cell is a device which converts solar power to electric power. It can be categorized, in material, to silicon type, compound type and organic type. It can also be categorized to bulk type and thin film type in other way. Take silicon type solar cell as an example, usually single-crystalline silicon solar cells and poly-crystalline silicon solar cells belong to bulk type while amorphous silicon solar cells and micro-crystalline solar cells silicon belong to thin film type.
The light absorption layer, the first conductive layer and the second conductive layer for a traditional thin film solar cells are substantially planar. Therefore the sunlight can't be reused as it is reflected by the second conductive layer and leave the solar cell. Some attempts have been put forward to increase the possibility for the incident sunlight to stay longer in the light absorption layer. For example, some method changes the path of the reflection light with a rough surface of the second conductive layer and the reflection light will be reflected totally back to the solar cell when it arrives at the cell-air interface. However, it does not happen on all of the reflected light. Another prior art tries to increase the possibility of a second reflection back to the light absorption layer for the reflected light by changing the path of the light in the light absorption layer (with a textured stack of first conductive layer, light absorption layer and second conductive layer, which is called as photovoltaic conversion structure in this document). However, it causes additional reflection loss of the incident sunlight when it arrives at the interface between the first conductive layer and the light absorption layer. As mentioned above, these methods improve the possibility to keep the incident sunlight staying longer in the photovoltaic layer only. Some reflected light still leaves the cell directly.